The human shoulder articulates about a loose fitting ball-and-socket joint which allows extremely free movement of the arm relative to the trunk. The ball is formed on the head of the humerus (the upper arm bone), and the socket is formed by the shallow, laterally opening glenoid cavity of the scapula (the flat triangular bone in the back of the shoulder). The depth of the socket is increased by a circumferential ring of fibrocartilage, the glenoid labrum, to which the head of the humerus is attached by an encircling mass of connective tissue called the articular capsule. Such capsule includes ligaments and tendons, for example.
There is little area of contact between the ball of the humerus and the glenoid cavity at any time. There always is a considerable part of the ball in contact with the articular capsule. The loose connection allows the articulating surfaces of the bones to be separated substantially. The joint is dependent for its integrity on the surrounding muscles. The joint is so loosely constructed that it is frequently dislocated, particularly by athletes participating in throwing or racquet sports.
There is greater superior (upper) and posterior (rearward) support for the shoulder joint so that it invariably dislocates in an anterior (forward) and inferior (downward) direction. The result is avulsion of the glenoid labrum from the anterior and inferior margins of the glenoid cavity, known as a Bankart lesion. A Bankart lesion can be detected by measuring the range of motion and verifying anterior instability of the shoulder joint.
Nonoperative treatment of anterior shoulder instability is rarely successful, but surgical repair almost always restores stability to the glenohumeral joint. Open shoulder surgery involves spreading the muscles overlying the anterior side of the joint and severing some of the connective tissue to provide access to the anterior glenoid rim. Typically, frayed tissue is resected and all tissue remnants attached to the anterior glenoid rim are debrided. The exposed bone is abraded. In one technique, intersecting holes are drilled in the anterior and lateral faces of the glenoid adjacent to the rim for sutures which secure the detached labrum firmly to the glenoid at two or three locations. Over time the labrum reattaches.
Arthroscopic surgery also is performed for repairing a Bankart lesion. Preparation of the glenoid rim to reduce it to a raw bleeding surface is essentially the same as for open surgery, but different techniques for securing the labrum to the glenoid area are used. In one technique, one or more staples are used to connect the glenoid labrum to the anterior side of the scapular neck medially of the glenoid cavity. In another technique, the labrum is impaled with a rivet which then is driven into the scapular neck. In another technique, blind bores are drilled adjacent to the anterior glenoid rim for specially designed suture anchors. In another technique, a hole is drilled through the scapular neck for suture material or for pins or screws to which suture material can be attached.
Often, full glenohumeral motion and, in the case of an athlete, performance are sacrificed for the stability restored by surgery. It is believed that one reason for inadequate stability, decreased motion and decreased performance is that the glenoid labrum is not secured at the anatomically correct location by use of known instruments and procedures. In some of the known techniques the labrum is secured to a single location such as an anchor member in the anterior side of the scapular neck, and in other known procedures the labrum is attached at two or three locations along only the anterior portion of the glenoid rim. Nevertheless, dislocation of the shoulder joint will tear the glenoid labrum from the inferior rim, as well as the anterior rim. Access to the inferior glenoid rim is limited, particularly during arthroscopic surgery. There is no known arthroscopic system that allows securing the labrum directly to the inferior glenoid rim, in addition to securing it along the anterior rim, so that the labrum will reattach in the correct position.